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Production of Radionuclides
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Cyclotron-Produced 1
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NMT Production of Ra
| Question | Answer |
|---|---|
| Production of Radionuclides | Cyclotron-Produced Reactor-Produced Radionuclide Generator |
| Cyclotron-Produced 1 | Charged particles accelerated and irradiate a target of stable elements Protons, deuterons, alpha, 3He |
| Cyclotron-Produced 2 | Incident particle may leave all or part of it’s energy in the target |
| Cyclotron-Produced 3 | Target nucleus becomes excited and emits nucleons in addition to a gamma ray leading to the formation of a different nuclide |
| cyclotron | particle accelerator used for the production of radioisotopes |
| Cyclotron Operation | entire process is controlled by a personal computer. |
| cyclotron consists of | a pair of hollow, semicircular metal electrodes (called "dees" because of their shape), positioned between the poles of a large electromagnet |
| radioisotope can be formed | by protons and neutrons from cyclotrons and nuclear reactors; nuclear reactions |
| man-made isotopes | are cyclotron isotopes and reactor isotopes |
| cyclotron isotopes | are formed by nuclear reactions with protons (from a cyclotron, a ring-shaped particle accelerator). |
| Reactor isotopes | are produced by nuclear reactions with neutrons which can only be generated in sufficient quantities during fission of uranium in a nuclear reactor. |
| Cyclotron-Produced - 111In produced | with 12 MeV protons 111Cd(p,n)111In 111Cd -- target p (proton) -- irradiating particle n (neutron) -- emitted particle 111In -- product |
| carrier-free | Radionuclides produced with atomic numbers different form those of the target do not contain any stable (“cold” or “carrier”) isotopes |
| Target | should be mono-isotopic |
| Isotopes | are then separated by chemical means solvent extraction, precipitation, ion exchange, and distillation |
| Cyclotron-Produced are | Usually neutron deficient Decays by positron emission or electron capture. |
| Cyclotron-Product | 123-Iodine Likely to be contaminated with 124I and 125I Indirect method -- 123Xe produced then decays to 123I 67-Gallium 111-Indium 201-Thallium |
| Short-Lived Cyclotron-Produced | Used mostly in PET (positron emission tomography), Cyclotron must be located on site. 11-Carbon 13-Nitrogen 15-Oxygen 18-Fluorine (FDG) |
| Reactor - Produced Radionuclides 1 | Fissile material fuel rods undergo spontaneous fission 235U and 239Pu |
| Reactor - Produced Radionuclides 2 | Neutrons emitted cause further fission Reaction controlled by cadmium rods in the core |
| Reactor - Produced Radionuclides 3 | Target elements are inserted in the core and interact with thermal neutrons to produce another nuclide |
| Reactor - Produced Radionuclides - Two types of interactions | Fission of heavy elements Neutron capture [ (n, g)] |
| Fission | breakup of a heavy nucleus into two fragments of approximately equal mass, accompanied by the emission of two to three neutrons with mean energies of about 1.5 MeV |
| Fission [(n,f)] Reaction - Heavy elements | atomic number greater than 92 235U, 239Pu, 237Np, 233U, 232Th |
| Nuclides | produced range in atomic number from 28 to nearly 65 |
| Fission [(n,f)] Reaction - Products | Products separated by chemical procedures Normally carrier-free with high specific activity Products usually neutron rich and decay by b- emission Products of 235U fission 131I, 99Mo, 133Xe, 137Cs |
| Neutron Capture [(n,g)] Reaction | Target captures a neutron and emits a gamma ray producing an isotope of the same element Not carrier-free, low specific activity Target and product same element, chemical separation unnecessary unless impurities develop |
| Neutron Capture [(n,g)] Reaction - Radionuclides produced | Radionuclides produced 131Te-131I 98Mo(n,g)99Mo 50Cr(n,g)51Cr Molybdenum-99 so produced is called “irradiated molybdenum” |
| Targets | 1000oC, water cooled, Designed in foil for heat dissipation-Copper, aluminum, uranium vanadium. Other forms - oxides, carbonates, nitrates and chlorides contained in aluminum tubing. Pneumatic tubes are often used to carry target to reactor or cyclotron. |
| Principles of a Generator | Decay-growth relationship Long-lived parent radionuclide and short-lived daughter radionuclide Chemical property of daughter is distinctly different from parent Easily transportable |
| Generator | Glass or plastic column fitted at bottom with fritted disk |
| Generator - column | is filled with adsorbent material cation-, or anion- exchange resin, alumina or zirconia on which the parent is absorbed |
| Generator - daughter | activity is eluted in a carrier-free state with an solvent |
| Generator - After elution | the daughter activity starts to grow again in the column until an equilibrium is reached. |
| Generator - Bacteriostatic agents | may be added to the column and a membrane filter attached to keep a sterile and pyrogen-free condition |
| Generator - “Milking the Cow” | Eluant is inverted onto needle A Evacuated vial is inverted onto needle B Vacuum in vial on needle B draws eluant through column and elutes the daughter nuclide, leaving the parent on the column |
| First commercial radionuclide generator was | 132Te -- 132I |
| Most important radionuclide generator in nuclear medicine is | the 99Mo -- 99mTc generator |
| 99Mo - decays | 87% decays to metastable 99mTc 13% decays to ground state 99Tc |
| 99mTc decays | by isomeric transition or gamma transition of 140 keV (10% are via internal conversion |
| 99Tc decays | by b- with a half-life of 2.1 X 105 years to 99Ru |
| 99Mo -- 99mTc Generator Construction | Liquid Column generator is rarely used in nuclear medicine and will not be discussed Solid Column Generator is used in modern day nuclear medicine |
| Solid Column Generator | “Moly” Generator, Alumina (Al2O3) loaded in a plastic or glass column, 99Mo is absorbed on alumina (MoO4-2, molybdate), Column is washed with isotonic saline, 99Mo is fission-produced |
| Solid Column Generator 99mTC | 99mTc will grow until maximum activity is reached after approximately four half-lives After maximum activity is reached 99mTc activity follows that of 99Mo (Fig. 5.2) 99mTc is eluted as sodium pertechnetate (Na99mTcO4) with 0.9% NaCl solution |
| Solid Column Generator - dry column | Isotonic saline is provided in vials of different sizes Evacuated vials are used to draw the saline through the column not leaving saline in the column |
| Solid Column Generator - wet column | Isotonic saline is provided in a bottle inside the generator Evacuated vials are used to draw the saline through the column leaving some of the saline in the column |
| Wet - Solid Column Generator | Radiation cause radiolysis of water in generator column result in formation of hydrogen peroxide (H2O2) & perhydroxyl free radical (HO2.), Radiolysis is more likely in high activity generators, Saline in tube may freeze extremely cold weather during ship |
| ATc = | = 0.956 (AMo)O(e-0.01034t - e-0.11550t) + (ATc)Oe-0.11550t |
| After transient equilibrium is reached | ATc = 0.956(AMo)t |
| 99Tc in the eluate | increases from 13% over time, this may cause reduction in labeling efficiency in radiopharmaceutical kits with small amounts of stannous ion |
| 99mTcHMPAO | the eluate must not be more than 2 hours old and the generator must have been eluted at least once in the past 24 hr. |
| Quality Control of 99mTc-Eluate | 99Mo Breakthrough Other Radionuclide Contamination Aluminum Breakthrough pH Radiochemical Purity |
| 99Mo Breakthrough | Small quantity of 99Mo may be eluted with the 99mTc NRC limit 0.15 mCi 99Mo/mCi 99mTc per administered dose at time of administration The eluate is shielded in lead to measure only the 740 and 780 keV 99Mo photons |
| Other Radionuclide Contamination | Other contaminants can be checked by a multichannel pulse height analyzer Usually performed by the manufacturer |
| Aluminum contamination | may come from the alumina bed of the generator |
| Aluminum interferes | with preparation of 99mTcSC and RBC tagging |
| Aluminum Breakthrough - Limits | 10 mg Al/ml of 99mTc |
| Detected by colorimetric method | Standard Al+ solution spotted on test strip 99mTc spotted on test strip Colors are compared, If 99mTc spot is denser than the standard there is excessive aluminum |
| pH | should be between 4.5 and 7.5 |
| Radiochemical Purity | Radiochemical impurities of the 99mTc eluate are all chemical forms of radioactivity other than 99mTcO4-. Described in Chapter 8. |
| Other Generators | 113Sn -- 113mIn 68Ge -- 68Ga 82Sr -- 82Rb 81Rb -- 81mKr |
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